1. Field of Invention
The present invention relates to distributed amplifiers and, in particular, distributed amplifiers suited for wide-band and high-power applications.
2. Description of Prior Art
Distributed amplifiers are widely used in part to overcome the gain-bandwidth limitation due to inherent capacitance of the active devices associated with the resistive loads. Inductors and transmission lines are commonly employed to resonate with the device capacitance. The combinations of inductors and capacitors are approximately equivalent to delay elements (e.g., transmission lines) and thereby increase the operational bandwidth. FIG. 1A shows a conventional distributed amplifier 10 comprised of an analysis module 20, a gain module 30 and a synthesis module 40. The gain elements of the gain module 30 are identical and uniformly distributed in conjunction with the inductors. An equivalent-circuit model of an elementary section 50 of the distributed amplifier 10 is shown in FIG. 18. The elementary section 50 is composed of two series inductors 51 and 52, and a shunt capacitance 53 in the format of a T-configuration. The inductors 51 and 52 are the inductors in the analysis 20 or synthesis module 40, while the capacitor 53 represents the device capacitance at the input or the output of the gain element. As the operation frequencies are lower than the resonance frequency of the components 51, 52, and 53, the elementary section 50 is approximately equal to a piece of transmission line 60 as shown in FIG. 1C. Virtually, a transmission line is a delay element with infinite bandwidth. Therefore, by combining device""s capacitance 53 with the inductors 51 and 52 into a transmission line 60, amplifiers with these types of analysis module and synthesis module can be operated over very wide frequency range. However, for the integrated circuit, the size of the inductor is comparably larger than the one for an active gain element. Moreover, the inductors in the analysis and synthesis modules are of two values, L and L/2, where L/2 is the inductance value on one arm of the T-configuration. This increases the complexity of the resulting design and implementation of the conventional analysis and synthesis modules. A simple architecture for the analysis and synthesis modules of the distributed amplifier is desirable and provided by the present invention.
The present invention is embodied as a circuit for a distributed amplifier where the analysis and synthesis lines are implemented in formats of a new xcfx80-configuration. In accordance with a preferred embodiment of the present invention, the connection of the inductors and the capacitive devices is in a format of a xcfx80-configuration, that is, two shunt device capacitances with a series inductor. The number of inductors is less by two than the number associated within a conventional distributed amplifier, in which the connection is in a format of a T-configuration. Moreover, according to the present invention, all the inductances of the synthesis, or analysis, lines are of the same value as opposed to the two different values in a conventional distributed amplifier. This sameness of value of the inductances is also present in the analysis lines of the present invention.
A distributed amplifier, according to the present invention, features compactness of integration and less complexity in designing the analysis and synthesis modules.